An electromechanical system in one example measures a parameter. The electromechanical system may comprise a micro-electromechanical system (“MEMS”) accelerometer or gyroscope that measures the parameter. For example, the accelerometer measures an acceleration and the gyroscope measures angular rate (e.g., rotation). The gyroscope in one example comprises a vibrating beam with high Q degenerate fundamental modes of oscillation. For example, high Q vibrating beams require little energy to sustain oscillation. The vibrating beam in one example is employable for high performance closed loop angular rate sensing. The gyroscope in another example is employable for lower performance open loop angular rate sensing. The mathematical model of the symmetrical vibrating beam is in many aspects similar to a vibrating ring or hemispherical. resonator gyroscope (“HRG”). The analytical similarity to the hemispherical resonator gyroscope indicates that the vibrating beam gyroscope has the potential of achieving similar performance.
The gyroscope comprises drive components coupled with the vibrating beam to cause a first oscillation of the vibrating beam. An angular rate of the vibrating beam and the first oscillation induce a Coriolis force on the vibrating beam. For example, the angular rate is about the longitudinal axis of the vibrating beam. The Coriolis force causes a second oscillation of the vibrating beam. The second oscillation is substantially perpendicular to the first oscillation. Feedback components in one example provide feedback on a magnitude of the first oscillation to the drive components for regulation of the first oscillation. Pickoff sensor components sense the second oscillations and apply control signals to null the pickoff signal. The control signals are a measure of the magnitude and polarity of the angular rate of the vibrating beam.
The vibrating beam in one example is supported by a frame. The frame connects with an outer surface of the vibrating beam. The frame allows movement of the vibrating beam upon occurrence of an angular rate. As one shortcoming, the frame absorbs a portion of the oscillation energy of the vibrating beam. The transfer of the oscillation energy from the vibrating beam to the frame reduces the oscillation energy of the vibrating beam. For example, the frame restricts motion of the vibrating beam and reduces the Q of the vibrating beam.
As another shortcoming, the gyroscope is sensitive to changes in the mechanical impedance of the structure to which the vibrating beam is mounted. This effect, known as mounting sensitivity, can result in gyroscope bias drift errors. The bias drift errors in one example result from changes in the mechanical impedance of the gyroscope housing and the structure to which it is mounted. Changes in mechanical impedance can be caused by changes in temperature giving rise to potentially large gyro bias drift temperature sensitivity.
Thus, a need exists for an angular rate sensing gyroscope that promotes a reduction in an amount of oscillation energy transferred from a vibrating beam to support components. A further need exists for an angular rate sensing gyroscope that promotes a reduction in sensitivity to changes in mechanical impedance of the vibrating beam mounting structure.